The author of these lines once had the pleasure of listening to a conversation between two Germanists who were discussing whether the word "genau" was superfluous in the German language. The logic says that if someone asks for the time or a distance, the addition "exactly" is unnecessary - after all, it is 7:47 p.m., or not, after all, it is 300 meters, or not. So are we just in time - or not - to have a conversation about accuracy? Indeed, when we speak of wavelengths, of distances measured in nanometers, the word "exact" quickly takes on a deeper meaning. And is it not a sign of German engineering to elevate precisely this accuracy to an art form?
We asked colleagues who need to know and talked to Alexander Einsle and Wolfgang Laube from Cognizant Mobility. Their projects are in the area of testing and deal with the development of test rigs used to measure windshields and head-up displays. The aim is to determine the specific properties of state-of-the-art head-up displays and the associated windshields for well-known car manufacturers. However, this measurement capability is only a preliminary stage. The next goals are easy-to-use lab test benches that should make it easier for OEMs to take high-precision (i.e., accurate!) measurements on components. Today we present what these projects are about, what there is to know about them - and why you sometimes take the file in your hand to make it even more accurate. Have fun!
Ca. 5 min
Head-up display testing: what it’s all about
Let’s stipulate, even if only for this article, that we do indeed need the word “accurate.” Finally, accuracy is important, especially when it is required by the customer. But how do we achieve this accuracy in the example of testing modern windshields onto which an image from a head-up display is to be projected? How do we generate the necessary measured values, and what is the way to display the test results? So long before we build the test bench or work on the test bench, we find that the knowledge gain is essential in the development of new test procedures, because there is simply no preliminary work, no briefing, no tutorial.
With the appropriate plan and in cooperation with the vehicle manufacturer, have been developed – also with the use of a file – a test bench prototype, on which can be placed front windows of vehicles. With the aid of a wide variety of measurements and data evaluation methods that are as accurate as possible, the specialists generate key figures that enable the properties of the windshield to be evaluated. Proof of the required properties is a prerequisite for the driver of a future car to see a brilliant image in the windshield generated by a head-up display in the depths of the dashboard.
For the head-up displays themselves, another separate test rig and sufficiently accurate measurement methods were developed to perform measurements that generate the raw data that serve as the basis for calculating the relevant key figures.
The combination of the capabilities of the two test rigs allows, especially in development, fast and objective assessments of different compositions of head-up displays and windshields.
Head-up display testing: what are special features?
Measurements are important and fun, but in any case require a high degree of accuracy. Some of these values can be in the nanometer range or in the range of fractions of a milliradian and, as already mentioned, there is no preliminary work. The head-up display test bench is the first of its kind and is intended to serve in the near future as a model for an easy-to-use laboratory test bench on which mass-produced head-up displays can also be easily tested in a short time. This is already the first special feature of this project: Where tests of HUDs have so far required hours, test times of less than 60 seconds are conceivable with the Cognizant Mobility test bench as the project continues to develop.
However, the interpretation of the measured data is also absolutely relevant. The fact that the measuring devices are brought into the correct positions in a fully automated and verifiable manner is so far unique and a real unique selling point of the Cognizant Mobility test bench.
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